The skeleton is the site for a number of different pathological lesions, e.g. primary and secondary malign tumours, benign tumours, infectious lesions, blood diseases etc. The lesions are often visible on X-ray pictures of the skeleton, but mostly it is not possible to asses the cause of the lesion by means of such X-ray pictures. In order to determine the nature of the lesion with certainty, portions of the bone must be taken out and examined under microscope.
Biopsy sampling in bone is difficult to carry out with the aid of a biopsy needle because the lesion often is delimited by the hard surface layer of the bone, i.e. cortical bone tissue.
Today essentially two methods are in use for taking biopsy samples from bone, namely operative biopsy and percutaneous needle biopsy. An operative ingress in most cases yields a good result, but frequently requires full narcosis, and in addition it is resource demanding and costly. Percutaneous needle biopsy is performed under local anesthesia, and the needle consists commonly of a sampling tube that is either provided with saw-teeth or is highly sharpened, and which is passed through the lesion, whereby a biopsy sample is cut or "punched" out. During insertion a stylet or needle (for the purposes of this application "stylet" and "needle" are regarded as synonymous) is placed in the tube, thereby creating a sharp distal tip of the tube for making the insertion through the softer parts easier. Examples of such needles are disclosed in EP-0 296 421 (the Ostycut needle) and in U.S. Pat No. 3,628,524 (the Jamshidi needle). These documents are incorporated herein by reference.
Existing biopsy needles have the considerable disadvantage that they may not be easily inserted into the bone because of friction between needle and bone. Biopsy needles such as Jamshidi or Ostycut all have a needle tip that can only penetrate thin or soft cortical bone due to the tip not cutting away material like a drill, but instead are to wedge there way in with great feeding force in combination with rotation.
Another disadvantage is that the large friction occurring between needle and cortical bone, makes the manipulation of the needle towards the target difficult, and causes development of heat which the patient may experience as painful. There are also needle types where the distal end of the needle has saw-tooth-shaped teeth. An example of such a needle is disclosed in U.S. Pat. No. 4,306,570 (the Corb needle). However, the drawbacks with saw teeth are that the teeth become clogged by drilling chips when drilling deeper than the height of the teeth. Furthermore the saw teeth must be protected by an outer protective tube during insertion through the soft portions of the body, in order not to cause damage, and this increases the required outer diameter of the needle.
In U.S. Pat. No. 4,543,966 there is disclosed a needle having a tip wherein the inner diameter of the tip is smaller than the inner diameter of the major part of the needle interior. The portion with reduced inner diameter at the tip has a longitudinal extension of 0.5-10 mm. The provision of such reduced inner diameter in the form of a cylindrical front end portion, is said to increase the amount of tissue sample that may be taken out, and also that the outer regions of the sample remains undamaged.
However, the cylindrical portion with reduced diameter causes some problem in that there may occur a stoppage or "jamming" of tissue at the intake opening, because of the friction in the narrow cylindrical portion.